During the past year, we completed a study in which we correlated plasma testosterone (T) levels with androgen receptors (AR), tissue content of T, and 5-alpha-dihydrotestosterone (DHT) present in the three anatomically-discrete lobes of intact and castrated Noble (Nb) rats bearing T-filled silastic capsules. We found that the proportion of nuclear/cytosolic AR as well as DHT:T levels were highest in the dorsolateral lobe (DLP) of intact rats. Furthermore, despite lower plasma and tissue T levels, the tissue content of DHT and cytosolic and nuclear AR, the weight and cytodifferentiation in all lobes of T-treated rats closely approximated values for intact rats. These findings may give insight into mechanisms which favor the development of prostatic carcinoma in the DLP of Nb rats bearing T-filled silastic implants. In addition, we have completed a study which demonstrates that the androgen-independent transplantable tumor line (A-I.T tumors) of Nb rats can respond to androgen. Treatment of tumor-bearing castrated rats with T for five days caused a marked enhancement of nuclear AR, DHT content which was paralleled by a 100% increase in cell division when compared with untreated controls. Marked differences in glycosphingolipid patterns and in protein-bound sialic acid were detected between histologically distinct regions of A-I.T tumors. These findings suggest the presence of at least two cell populations within the neoplasm which have differing states of cell surface and membrane differentiation. Twenty-one hour organ cultures of A-I.T tumors demonstrated that 8.5 mM of added androgen may enhance levels of 5-alpha-reductase, the terminal 3-beta-hydroxysteroid pathway, and [3H] 5-alpha-DHT binding to nuclear sites. (D)